Nitramine, nitrocellulose explosive with ester plasticizer



United States Patent 1 O 3,311,513 NITRAMINE, NITROCELLULOSE EXPLOSIVE WITH ESTER PLASTICIZER Charles Donald Forrest, Westville, N.J., assignorto E.- I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 5, 1965, Ser. No. 437,555

8 Claims. (6]. 1492) This invention is concerned with improved detcnating explosive compositions that combine desirable. explosive properties with such physical-mechanical characteristics as flexibility, high resistance to compressive and tensile forces and good low ten'iperature properties, and with improved shaped explosive articles obtainable therefrom.

It has long been a goal in the art of explosives to provide detonating explosive compositions that not only possess-high sensitivity to detonation by standard explosive initiators, coupled with low sensitivity to initiation by impact, but also meet the requirements of a high degree of dimensional stability under stress, coupled with good flexibility. However, only in recent years has any real success been achieved in this field, particularly in terms of ability to maintain these desired explosive and physical characteristics over a wide range of environmental conditions.

One recently developed type of flexible, yet dimensionally stable, detonating explosive composition is described in U.S. Patent 2,992,087. Compositions described therein include at least about 44% by weight of the crystalline explosive, pentaerythritol tetranitrate (PETN), of specified very fine particle size, in admixture with a binder composition of about 6.5 to 14% by weight of soluble nitrocellulose of average degree of polymerization about 2000 to 3000 and about 15 to 35% of selected trialkyl esters of Z-acetoxy-1,2,3-propanetricarboxylic acid.

As is demonstrated in US. Patent 2,992,087, the PETN-containing compositions described therein have many advantages from the point of View of physical characteristics. They are readily formulated, and the rheological properties of the finished compositions are such as to permit easy forming, e.g., by rolling or extrusion, into shaped articles'of various configurations. The shaped products themselves are characteristic bv a high degree of flexibility and good dimensional stability understress, even after subjection to serve environmental conditions such as prolonged exposure to high temperatures and to Water, including exposure at high hydrostatic pressures. The compositions of US. Patent 2,992,087 also have, and maintain, a desirable combination of explosive properties.

Even though these compositions will prop-agate a detonation reliably, even in sheets as thin as inch and thinner and are very insensitive to initiation by impact, the PETN-co-ntainin-g compositions of US. Patent 2,992,087 have been found to have several disadvantages. High loadings or concentrations of crystalline high explosive are desirable for certain applications of this type of charge. However, when an attempt is made to employ PETN loadings above about 65% by Weight of the total composition, blending of the charge components and shaping or forming of the finished products both become increasingly difficult operations. Also, when fabricated, for example, into cords or sheets, the composi- Lions containing these high loadings of P ETN show increasing brittleness with increasing PETN content, even at ambient temperatures, but particuiarly when exposed to subzero temperatures. Hence today tend to crack, craze and split when subjected to flexural stresses at low temperatures. Additionally, when the known PETN-containing compositions are formulated so that they do possess optimum physical characteristics, including flexi bility, the detonation velocity of such compositions generally does not exceed about 7000 meters per second, which is lower than desired for some applications of this type of charge. In some instances, the requirement that ultrafine crystals of PETN be used in the compositions of US. Patent 2,992,087 in order to achieve propagation reliability and uniformity of explosiveproperties can be a disadvantage. A further limitation is imposed by the need to use one specific class of plasticizer esters, if the explosive compositions are to perform reliably, particularly after exposure to elevated temperatures.

This invention provides improvments in detonating explosive compositions comprising crystalline organic high explosives in a binder composition ofnitrocellulose and selected plasticizers. More particularly, the invention provides improvements in the subject type of explosive compositions whereby highly desirable physical and explosive properties, including properties not achievable heretofore, are obtained, The invention additionally provides new and improved methods for preparing said explosive compositions.

The improved de'tonating explosive compositions of this invention, which are readily worked into self-supporting and dimensionally stable, yet flexible articles, e.g., sheets, cords, tapes and the like, comprise uniform blends of:

(1) about from to preferably about from 68 to 80% by Weight of crystalline explosive nitramine having an average particle size below about 200 microns, and preferably below about microns and selected from the group consisting of -cyclotrimethylenetrinitramine and cyclotetramethylenetetranitramine;

(2) about from 0.5 to 15%, and preferably about from 2 to 8% by weight of soluble nitrocellulose having an average degree of polymerization of about from 2000 to 3000; and

(3) about from 10 to 34.5%, and preferably abou from 12 to 30% by weight of ester selected from phosphateand carboxylate esters having the formulas:

in which each R (i.e., each R can be the same or different from the other Rs) represents an aliphatically saturated organic radical of about 1 to 8 carbon atoms free of functional substituents, i.e., inert in the system; is a hydrocarbon nucleus of about 1 to 8 carbon atoms; and each of m, n, and q is a cardinal number of 0 to l, the sum of n, p, and q being 2 to 3.

The crystalline high explosive component of the compositions of this invention is chosen from the organic explosive nitramines, cyclotrimethylenetrinitramine and cyclotetramethylenetetranitramine. As is shown more fully hereinafter, these crystalline explosive nitramines have been found to be unique in their ability to impart certain highly desirable characteristics to shaped explosive products prepared therefrom. The subject nitramines, which are known by several alternative designations. have the structural formulas:

Cyclotrimethylenetrinitramlne Alternative common names: RDX, hexagen, cyclonite Chemical name: Hexahydro-l,3,5-trinitro-s-triazene Cycltetramethylenetetrauitramine Alternative common names: HMX, octogen, homocyclonite Chemical name: Octobydro-1,3,5,7 tetranitro l,3,5,7-

tetrazocine These nitrarnines can be used individually in the explosive compositions of this invention, but they also are suitably employed in combination. For example, the mixed nitramine products that are obtainable by subjecting hexamethylenetetrarnine, or the precursors, formaldehyde and ammonium nitrate, to nitrolysis processes can be used in lieu of the substantially pure individual nitramines.

As indicated hereinbefore, the concentration or loading of explosive nitramine will generally be about from 65 to 85% of the total weight of the explosive composition. Concentrations of explosive nitramine appreciably below this range, in addition to imparting lower densities and lower explosive strengths per unit weight of charge, make the charges increasingly insensitive to initiation. Also, even when suitably initiated, such low-concentration charges often fail to propagate a detonation, or the detonation may proceed at low velocity.

On the other hand, explosive nitramine loadings above about 85% make the compositions increasingly difficult to mix and shape and, at thesame time, tend to impart less than optimum physcial characteristics to the finished products. An optimum balance of explosive characteristics and physical properties has been found to be present in shaped explosive products when the explosive nit-ramine concentration is about from 68 to 80% of the charge weight. Accordingly, this latter concentration range is especially preferred in the instant explosive compositions.

Shaped explosive products of satisfactory sensitivity to initiation are obtained when the explosive nitramine component is in the form of crystals having an average particle size below about 200 microns. (Average particle size, as used herein, means weight average particle size, as calculated from standard sieve analysis values and from microscopic measurement values for particles generally smaller than the standard 325-mesh sieve apertures of 43-44 microns.) In general, however, superior initiation sensitiveness is achieved when the average particle size is below about 100 microns, and preferably about from 1 to microns. Thus, nitramine crystals of these relatively smaller particle sizes are generally preferred in the instant compositions.

The nitrocellulose used in the explosive compositions of the instant invention will be one of high-viscosity, soluble types. To meet the requirement of high viscosity, the average degree of polymerization, or average number of anhydroglucose units in the nitrocellulose molecules, will be in the range of about from 2000 to 3000. To provide the necessary solubility, by which in the nitrosellulose art is meant solubility in a mixture of ethyl ether and ethyl alcohol, the nitrocellulose also will have a nitrogen content generally above 7% and usually above about 9%, but below 13%. Provided that these two requirements are met, any of the industrial grades of nitrocellulose, which ordinarily have a nitrogen content in the range of about 10 to 12.3%, as well as the pyrocottons, which generally have a nitrogen content of 12% or higher, can be used. High-viscosity, soluble grades of nitrocellulose having a nitrogen content of about 12.2 to 12.6%, such as are ordinarily used in the formulation of dynamites, constitute a readily available and especially suitable form of the nitrocellulose in the instant compositions.

Shaped explosive products having desired physical and explosive characteristics are obtained when the concentration of nitrocellulose is at least about 0.5% of the total charge weight. On the other hand, nitrocellulose concentrations above about 15% of the total composition make increasingly difficult the incorporation of this component into the compositions, and do not materially improve either the explosive or the physical characteristics of the products over those achieved at lower concentration levels. A particularly preferred range of concentration for the nitrocellulose, especially when the explosive nitramine loading is in range of about 68 to is about from 2 to 8% of the total composition.

The nitrocellulose plasticizer chosen for the compositions of this invention is of primary importance, in that such plasticizer not only affects the physical and explosive characteristics of the product in the as-made state but also, and more significantly, influences the retention of these properties over a wide range of environmental conditions. Numerous plasticizers for nitrocellulose are known. However, for satisfactory performance of the instant explosive compositions over a temperature range of 40 to F., it has been found that plasticizers of both the phosphate ester and carboxylate ester types are uniquely suitable. These plasticizers can be described by the general formulas:

in which each R represents an aliphatically saturated organic radical of about 1 to 8 carbon atoms free of functional substituents, preferably, a saturated hydrocarbon radical; is a hydrocarbon nucleus of about 1 to 8 carbon atoms; and each of m, n, p and q is a cardinal number of 0 to 1, inclusive, the sum of n, p and q being 2 to 3. (By free of functional substituents, it is meant that the molecules of the organic monohydroxy compound or compounds from which the phosphate and car- =boxylate esters are derived shall be free of reactive groups other than the OH function.)

Within the ester groups represented by the foregoing formulas, optimum properties are generally achieved in the finished explosive products when R is a saturated aliphatic acyclic or cyclic radical containing about from 4 to 8 carbon atoms. As previously indicated, the in dividual Rs can be like or different. Likewise, it is preferred that the hydrocarbon nucleus, represent either a saturated hydrocarbon nucleus, particularly an acyclic saturated hydrocarbon nucleus, or a benzenoid nucleus containing up to about 8 carbon atoms. Compatability with nitrocellulose tends to decrease when such organic nuclei, and/or the organic portions of the hydroxy compounds from which the ester plasticizers are prepared, contain more than about 8 carbon atoms.

A representative but not exhaustive group of specific ester plasticizers that can be used effectively, either alone or in combination, in thepresent explosive compositions includes:

triethyl phosphate tributyl phosphate tris(2-ethylhexyl) phosphate tris(tetrahydrofurfuryl) phosphate bis(Z-ethylhexyl) adipate diisoctyl adipate bis(Z-ethylbutyl) azelate bis(Z-ethylhexyl) sebacate di-n-butyl phthalate diisobutyl phthalate bis(Z-ethylhexyl) phthalate triethyl 2-acetoxy-1,2,3-propanetricarboxylate tri-n-butyl 2-acetoxy-l,2,3-propanetricarboxylate tris(2-ethy1hexyl) Z-acetoxy-l,2,3-propanetricarboxylate Among these esters, tributyl phosphate, dibutyl pht-halate, bis(2-ethylhexyl) adipate, bis(2-ethylhexyl) sebacate, and especially, tributyl Z-acetoxy-1,2,3-propanetricarboxylate, are particularly effective and are preferred.

In selecting any particular plasticizer from the above group for any particular composition of this invention, or a plasticizer mixture therefor, several criteria should be observed. The plasticizer should both have a negligible, i.e., a low, rate of evaporation in the composition, and be liquid over the temperature range of use, e.g., 40 to +16O F. The plasticizer in addition to having a low solubility in and solvent power for water, should be substantially a non-solvent for the particular nitramine selected. Conversely, the plasticizer should be at least partially miscible with the grade of nitrocellulose employed, and preferably completely miscible therewith. Finally, in the particular composition in which it is used, the plasticizer should maintain relatively constant properties with time and over the temperature range to which it is to be exposed. Some helpful guides for selection within the aforementioned unique group can be obtained from Chapter of The Technology of Solvents and Plasticizers by A. K. Doolittle, New York, John Wiley and Sons, Inc. (195 4).

The concentration of ester plasticizer in the explosive compositions will generally be about 10 to 34.5% by weight, and preferably about from 12 to 36%. When the nitrocellulose concentration is in the preferred range of about from 2 to 8%, and especially when the nitrocellulose constitutes 4% by weight or less of the total explosive composition, optimum product flexibility at low temperatures, including subzero temperatures, usually has been found to be achieved by employing an ester plasticizer-to-nitrocellulose ratio of at least about 4/1.

' The explosive compositions of this invention can be prepared by several methods, including the procedure of the aforementioned U.S.P. 2,992,087, wherein waterwetted crystalline high explosive is blended with the plasticizer ester, generally at an elevated temperature, and then the blend, preferably after being freed of excess water, is intimately mixed with the nitrocellulose. However, it has been found that the finished explosive products have improved uniformity and, more particularly, are consistently obtained free of voids, air bubbles, and similar inhomogeneities, when a uniform blend of a portion of the crystalline explosive nitramine and the plasticizer ester is first formed; this is blended with the nitrocellulose until substantially no lumps or inhomogeneities (uncolloided nitrocellulose) are present therein; and finally the remaining part of the crystalline explosive nitramine is incorporated, in one or more portions, and blending is continued until the mass is uniformly mixed and preferably is in the form of small unconsolidated granules.

In following the said improved method of preparing the explosive compositions, the quantity of crystalline explosive nitramine incorporated in the first blending operation will generally be about from 50 to by weight of the total nitramine to be used in the formula, and preferably about from 65 to 85% of the total nitramine. The remaining 10 to 50% of explosive nitramine subsequently added to the mass free of uncolloided nitrocellulose is incorporated in one or more portions, and mixing is continued until a granular but non-consolidated product is obtained. To facilitate blending, the mixing operations ordinarily are carried out at elevated temperatures, generally in the range of about from to 150 F., and preferably about from to F.

The explosive nitramine can be incorporated into the compositions in a substantially dry state. However, to minimize dusting of the crystalline explosive and also to reduce its impact sensitivity and associated hazards during the manufacturing operation, it is advantageous to have the nitramine in a wetted state during its incorporation. The wetting agent can be a liquid which has substantially no solvent power either for the explosive nitramine or for the remaining composition components. Water is particularly suitable in this capacity, not only because it meets the nonsolvent criterion, but also because it is relatively easily removed following incorporation of the nitramine.

A modification of the foregoing wetting method for minimizing dusting and impact sensitiveness in the explosive nitramine also has been found to be effective, particularly in cases where the crystalline nitramine consists of moderately fine to very fine particles, i.e., is below about 100 microns in average particle size. This modification, which also avoids any need for introduction and subsequent removal of a foreign liquid wetting agent during processing, involves the use of the explosive nitramine in the form of crystals having a preformed coating of one of the aforementioned plasticizer esters. To be effective, especially with respect to reducing impact sensitivity, the coating on the explosive crystals will generally constitute at least about 5% by weight thereof, and can range up to about 25% of the total weight of nitramine and ester. The advantages of using ester-coated crystalline nitramine in terms of safety during manufacture of the instant explosive compositions can be seen from the following tabulated drop-test data. In each case, the particular explosive nitramine is taken from the same lot of very fine material all below 44 microns), and the coating agent is the tri-n-butyl ester of 2-acetoxy-1,2,3-propanetricarboxylic acid, used in the specified concentration. The drop tests, a standard method of measuring sensitiveness to initiation of detonation by impact, are conducted with a modification of the apparatus described in U.S. Bureau of Mines Bulletin 346 (1931). In the tests, the maximum height from which the impacting weight (5 kg.) falls on the test specimen is 56 inches, and the test samples are placed in .a small metal cup rather than directly on the anvil. Impact sensitivity is reported as the minimum distance of weight drop (in inches) that causes detonation in 50% of the samples (20 trials in each case). (Samples that consistently fail to detonate when the weight is dropped from the maximum height of 56 inches are reported to have a sensitivity of 56+ inches.)

lulose is sensitive to ignition by static charges.

Cyclotrimethylenetrinitramine Wt. percent of Ester: Impact sensitivity (inches) CyclotetramethyIenetetranitramine Wt. percent of Ester: Impact sensitivity (inches) While other materials such as Waxes and oils have been used effectively to desensitize the subject explosive nitramines per se, the presence of substantial quantities of such additives in the explosive compositions of this invention has a deleterious effect on the properties of the finished explosive products, especially on their physical-mechanical characteristics at elevated temperatures l F.) Accordingly, it is preferred in the present compositions to confine the desensitizing agents for the explosive nitramine to the aforedescribed nonsolvent wetting liquids and esters. The latter materials are especially advantageous in that they simiultaneously serve the dual functions of nitrocellulose plasticizer and explosive nitramine desensitizer.

Depending on the particular mixing procedure employ, all or a portion of the explosive nitramine used in the instant compositions can be in the form of crystals provided with a coating of the aforementioned esters. The proportion of ester incorporated in the form of such coating can constitute as little as about one-sixth of the total ester to as much as 100% thereof. Accordingly, Where necessary, supplemental portions of uncombined ester are used.

The nitrocellulose used in the explosive compositions can be wetted with alcohol, with water, or with combinations of the two. However, it has also been found suitable and advantageous in certain cases to incorporate substantially dry nitrocellulose. (Warning: Dry nitrocel- Accordingly, personnel and manufacturing equipment and facilities should be appropriately protected when the form of nitrocellulose is used.) Employing dried nitrocellulose is of particular merit when ester-coated crystalline nitramine is also employed, as the need for removal of any foreign wetting agents during processing is thereby entirely avoided.

The generally granular explosive products obtained by blending the components in the aforedescribed manner are readily converted into compact, self-supporting yet flexible articles such as sheets, tapes, cords, blocks and other rectilinear and curvilinear shaped articles, including those of relatively complex configuration, e.g., having V-grooves or cavities therein as well as those, such as sheets or blocks, of relatively plain configuration. The shaping can be accomplished by pressure molding, rolling extrusion, and similar forming operations, and can be conducted at ambient or elevated temperatures, depending on the particular composition and type of forming involved. The shaped articles can thus be obtained in a variety of shapes and thicknesses or diameters. In addition, they are easily cut or sliced to give special configurations not obtained by the usual forming procedures. Of the aforementioned shaped explosive products, sheets that are about from 0.05 to 0.50 inch in thickness and have a loading of about from 1.3 to 14.0 grams per square inch of surface area and cords that are about from 0.125 to 0.75 inch in diameter and have a loading of about from 0.3 to 1.2 grams sheets and cords make optimum use of the outstanding properties of the products of this invention.

The following examples provide specific illustrations of the explosive compositions of this invention, their explosive and physical characteristics, and their advantages. In the examples, parts and percentages reported are by weight.

EXAMPLES 1 TO 6 The compositions of following Table I are produced in a mixer provided with an agitator, a water jacket for heating, and means for measuring temperature within the mixer charge. In each case, the crystalline explosive nitramine, cyclotrimethylenetrinitramine (referred to as RDX in the table), is premixed at about F. with approximately 15 to 20% of water, and a portion of the wet nitramine ranging from about 15 to 25% of the total is removed from the mixer. The portion of heated, wet nitramine remaining in the mixer thereafter is blended for several minutes with the tributyl ester of 2-acetoxy-l,2,3- propanetricarboxylic acid (designated ester in the table) until a uniform mixture is obtained. Free water in the mixture then is decanted, and a small amount (0.2-0.5 of the total composition) of an inert pigment or dye, e.g., lead chromate, is added, if desired, to impart a distinctive color to the final composition. Three portions of highviscosity, soluble nitrocellulose (NC in the table) having a nitrogen content of about 12.3% and a degree of polymerization around 3000 then are incorporated at intervals of a few minutes, the portions constituting about onehalf, one-fourth, and one-fourth of the total nitrocellulose, respectively. Heating, at the specified temperature, and agitation are maintained during and after this addition until all lumps or inhomogeneities are gone, signifying the absence of uncolloided nitrocellulose, and until the mixture is substantially water-free. The remaining portion of the wet crystalline cyclotrirnethylenetrinitramine then is incorporated, and the mixture is maintained at about 130 F. with agitation for several additional minutes, until the mass is converted into small, substantially dry nonconsolidated granules. Finally the granular mass is removed from the mixer and passed to an extruder to form tough yet flexible sheet explosive products characterized by a high degree of uniformity in thickness, composition, and consistency.

In Table I, the formulas of Examples 1 to 4, inclusive, contain very fine crystals of cyclotrimethylenetrinitrarnine (average particle size, 7-10 microns), whereas the formula of Example 5 contains crystals of somewhat larger size (average particle size, 70-80 microns), and that of Example 6 contains relatively coarse crystals (average particle size, -180 microns).

TABLE I Example 1 2 l 3 y 4 y 5 6 Percent RDX 68 70 72 75 70 70 Percent Ester- 26 25 24 20 25 25 Percent NO 6 5 4 5 5 5 TABLE II Example 1 2 3 4 5 6 Density, g./cc 1. 52 1. 52- 1. 53 1. 58 1. 51 1. 53 Detonattioi Test:

ia or B a Velocity of Detonation, meters/ sec. 7, 250 7, 460 7, 250 7, 460 7, 170 6, 670

a Blasting cap with base charge of12 grains of PETN. Blasting cap with base charge of 9 grains of PETN. a 8-gram pellet of waxed cyclotrimethylenetrinitramine.

Sheet explosive products having similar explosive and physical characteristics are obtained when one of the esters, tributyl phosphate, dibutyl phthalate, bis(2-ethylhexyl) adipate, or bis(2-ethylhexyl) sebacate, is substituted on an equivalent weight basis for the tributyl Z-acetoxy-1,2,3-propanetricarboxylate in the formulas of the above tables. These formulas also can be shaped into tough yet resilient and flexible sheet products by cold or hot rolling procedures, or alternatively, they can be converted into tapes, cords, and similar configurations, for example, by extrusion through suitable dies.

EXAMPLE 7 Following the general procedure of Examples 1 to 6, a composition of 70% cyclotetramethylenetetranitramine having an average particle size in the 1215 micron range, 22% of tributyl Z-acetoxy-1,2,3-propanetricarboxylate,

and 8% of the high-viscosity, soluble nitrocellulose of the compositions of Examples 1 to 6 is prepared by first adding all the tributyl ester to the fine-particle cyclotetramethylenetetranitramine and allowing the mixture to stand for a period sufiicient for the ester to coat and soak into the nitramine crystals. At a temperature of approximately 140 F., the nitrocellulose, in water-wet state, then is incorporated into the coated crystals in approximately three equal portions. Mixing is continued at the specified temperature until the nitrocellulose is thoroughly blended in and the mixture is substantially dry. The mass then is removed from the mixer and extruded through dies to form explosive cords of various diameters. One cord product so obtained has a diameter of 0.460 inch and a density of 1.58 g./cc. When initiated with the aid of an 18-gram pellet of waxed cyclotrimethylenetrinitramine, a 44-inch length of this cord detonates completely at a velocity of 7350 meters per second.

Finished cyclotetramethylenetetranitramine-containing explosive products of substantially the same physical and explosive properties are obtained when the foregoing procedure for preparing the subject formula is modified by withholding from the blending process a portion of the ester-coated cyclotetramethylenetetranitramine, e.g.,

about from 10 to 25% thereof, until after the nitrocellulose is added and thoroughly blended in. The more granular product so obtained is, however, somewhat easier to handle and fabricate into void-free shaped articles such as cords, tapes, and sheets.

EXAMPLES 8 to 10 perature of about 140 F., the total quantity of nitrocel-.

lulose (NC) specified is added in dry form in several mi iheets 0.160 inch in thickness are used except for Example 6, where the sheet is 0.320 inch portions to that part of the cyclotetramethylenetetranitramine-ester mixture remaining in the mixer, and mixing is continued at the same temperature until the mass is substantially free of uncolloided nitrocellulose. The portion of the cyclotetramethylenetetranitramine-ester mixture previously reserved is incorporated into the mixture, and the resulting mass is agitated until small, nonconsolidated granules are obtained. During the last few minutes of mixing, the mixer is maintained under vacuum to allow entrapped air to escape from the mass. The product then passes to an extruder that is fitted with dies of various sizes to prepare cord products ranging from 1 Substantially all particles smaller than 50 microns; average particle size less than 8 microns.

Explosive characteristics of the foregoing compositions are assessed by determining the densities of the cord products (at the same diameter and at equivalent weight loadings per unit of length) and by measuring the detonation velocities of the cords when initiated by a lO-gram PETN primer. These values are reported in Table IV, in which the example designations refer to those of Table III.

TABLE IV Example 8 9 10 Density, g./cc 1. 64 1. 67 1. 69 Velocity of Detonation, meters/sec;

0.125-in. cord 7, 350 7, 620 8, 020 0.187-iu. cord 7, 640 7, 875 8, 0.250in. cord 7, 975 8, 8, 250

EXAMPLES 11 to 15 Following Table V reports explosive and physical characteristics of several explosive compositions of this invention, together with characteristics of explosive compositions of the type disclosed in U.S.P. 2,992,087. The crystalline high explosives used in the compositions of Table V are of comparable very fine particle size, i.e., substantially all of the particles are smaller than 44-50 microns. The average particle size of the PETN is about 7 to 10 microns, and that of the cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX) is 8 microns or less. The ester in the compositions of Table V is tributyl Z-acetoxy-l,2,3-propanetricarboxylate.

s, a 1 1, 1 e

1 q l l 4..

TABLE V Flexibility at- Density, VOD, Compositions of This Invention g./cc. meters/sec.

Ambient Low Temp.

Temp.

11. 63/29/8% RDX/Ester/NC 1. 48 Goog a%-40 F. and 12. 68/26/6% HMX/Ester/NO 1. 52 Do. 13. 70/22/8% I'lMX/Ester/NCuh 1.58 Good, at 37 F. 14. 72/23/5% RDX/Ester/NO 1. 55 Gool, a%40 F. and

5 15. 80/l7.5/2.5% HMX/Ester/NC 1. 64 Good, at -40 F. Compositions of U.S.P. 2,992,087 (for Comparison):

A. 63/29/8% PETN/ESter/NO 1.43-1.46 6, 700-6, 900 do Gooi ag 40 F. and

B. 67/27/6% PETN/Ester/NC... 1. 47 6, SOD-7,000 P001, at -20 F.

C. 71/24/5% PEIN/Ester/NC 1. 48 7, 000 a Poor, at l0 F.

D. 80/17.5/2.5% PE'lN/Ester/NC 1.53 Poor, at 40 F.

n Velocity of detonation.

b Flexibility at ambient temperature (about 70-75 F.) is determined by manual twisting and bending of the sheet or cord product in the as-made state. Low-temperature flexibilities are determined after at least several hours storage of the sheet or cord at the indicated subzero temperature or temperatures. The low-temperature test results reported are based on a quick folding of the chilled specimen around a 54-inch wood dowel so that it is bent back on itself essentially 180, followed by immediate visual inspection of the sample for erazing, cracks and similar flaws. In the table, good indicates absence of brittleness and flaws; iair" means moderate brittleness; and poor indicates significant brittleness and cracking-craziug flaws.

e Cord product is too fragile to permit detonation velocity determinations on -15 inch lengths generally used for this test.

As can be seen from the data of Table V, the compositions of this invention containing the crystalline explosive nitramines, cyclotrimethylenetrinitramine and cyclotetramcthylenetctranitramine, are generally superior to similar explosives containing PETN in density and in velocity of detonation at each level of high explosive loading exemplified. The compositions of this invention, particularly those containing high explosive loadings on the order of 68 to 80% of the total composition weight are, in addition, markedly superior to the comparable PETN-containing compositions in their ability to withstand exposure to normal and low (Subzero) temperature Without becoming so brittle as to be inflexible and subject to cracking and crazing. The compositions of the instant invention thus make it possible to employ these high explosive loadings and to enjoy the attendant advantages of high density and high velocity of detonation without sacrifice in the physical-mechanical characteristics of the compositions at normal and low temperatures.

What is claimed is:

1. Improved detonating explosive compositions comprising uniform blends of z (a) about from 65 to 85% by weight of crystalline explosive nitramine having an average particle size below about 200 microns and selected from the group consisting of cyclotrimethylenetrinitramine and cyclotetramethylenetetranitramine;

(b) about from 0.5 to by weight of soluble nitrocellulose having an average degree of polymerization of about from 2000 to 3000; and (c) about from 10 to 34.5% by weight of ester selected from phosphate and carboxylatc esters having the formulas:

i E (0o-oiii)m RO1|OR and (o0oR).. OR (O 0 0 R) (C O OR q in which each R represents an aliphatically saturated organic radical of about 1 to 8 carbon atoms free of functional substituents; is a hydrocarbon nucleus of about 1 to 8 carbon atoms; and each of m, n, p, and q is a cardinal number of 0 to l, the sum of n, p, and q being 2 to 3.

2. A sheet explosive of the composition of claim 1.

3. A detonating cord of the composition of claim 1.

4. An improved detonating explosive composition comprising a uniform blend of:

(a) about from 68 to 80% by weight of crystalline explosive nitramine having an average particle size below about 100 microns and selected from the group consisting of cyclotrimethylenetrinitramine and cyclotetramethylenctetranitramine;

(b) about from 2 to 8% by weight of soluble nitrocellulose having an average degree of polymerization of about from 2000 to 3000; and

(0) about from 12 to 30% by weight of tributyl ester of Z-acetoxy-1,2,3-propanetricarboxylic acid.

5. A detonating explosive composition of claim 4 wherein the crystalline explosive nitramine has an average particle size of about from 1 to 75 microns.

6. In a method for preparing improved detonating explosive compositions comprising uniform blends of:

(a) about from 65 to 85% by weight of crystalline explosive nitraminc having an average particle size below about 200 microns and selected from the group consisting of cyclotrimethylcnetrinitramine and cyclotctramcthylenctetranitraminc;

(b) about from 0.5 to 15 by weight of soluble nitrocellulose having an average degree of polymerization of about from 2000 to 3000; and

(c) about from 10 to 34.5% by weight of ester selected from phosphate and carboxylate esters having the formulas:

o O (O 'C I3)rn RO-i 0R and ]-l(cooa n (I)R (00011) (c 0 o R) q in which each R represents an aliphatically saturated organic radical of about 1 to 8 carbon atoms free of functional substituents; is a hydrocarbon nucleus of about 1 to 8 carbon atoms; and each of m, n, p, and q is a cardinal number of 0 to l, the sum of n, p, and q being 2 to 3,

the steps comprising intimately blending about from 50 to of the total weight of said crystalline explosive nitramine with said ester and said nitrocellulose until a first substantially homogeneous mass is formed, then intimately blending the remaining por- 70 tion of said nitramine with said first mass until a uniform product is obtained.

7. A method according to claim 6 wherein the crystalline explosive nitramine has an average particle size below about microns; the ester is tributyl 2-acetoxy-l,2,3-

5 propanetricarboxylate; and the crystalline explosive nitramine introduced in said blending operations is precoated with about from 5 to 25% of said ester, based on the total weight of nitramine and ester.

8. Crystals of explosive nitramine having an average particle size below about 100 microns and selected from the group consisting of cyclotrimethylenetrinitramine and cyclotetramethylenetetranitramine, said crystals being coated with about from 5 to 25% of tributyl 2-acetoxy- 1,2,3-propanetricarboxylate, based on the total Weight of nitramine and carboxylate.

References Cited by the Examiner UNITED STATES PATENTS 3,227,588 1/1966 Jones et .al. 149-92 X 3,235,420 2/1'9 66 Murphy 149-92 X CARL D. QUARFORTH, Primary Examiner.

References Cited by the Applicant UNITED STATES PATENTS L. DEWAYN-E R'UTLEDGE, Examiner.

S. LECHERT, Assistant Examiner. 

1. IMPROVED DETONATING EXPLOSIVE COMPOSITIONS COMPRISING UNIFORM BLENDS OF: (A) ABOUT FROM 65 TO 85% BY WEIGHT OF CRYSTALLINE EXPLOSVIE NITRAMINE HAVING AN AVERAGE PARTICLE SIZE BELOW ABOUT 200 MICRONS AND SELECTED FROM THE GROUP CONSISTING OF CYCLOTRIMETHYLENETRINITRAMINE AND CYCLOTETRAMETHYLENETETRANITRAMINE; (B) ABOUT FROM 0.5 TO 15% BY WEIGHT OF SOLUBLE NITROCELLULOSE HAVING AN AVERAGE DEGREE OF POLYMERIZATION OF ABOUT FROM 2000 TO 3000; AND (C) ABOUT FROM 10 TO 34.5% BY WEIGHT OF ESTER SELECTED FROM PHOSPHATE AND CARBOXYLATE ESTERS HAVING THE FORMUALS:
 6. IN A METHOD FOR PREPARING IMPROVED DETONATING EXPLOSIVE COMPOSITIONS COMPRISING UNIFORM BLENDS OF: (A) ABOUT FROM 65 TO 85% BY WEIGHT OF CRYSTALLINE EXPLOSIVE NITRAMINE HAVING AN AVERAGE PARTICLE SIZE BELOW ABOUT 200 MICRONS AND SELECTED FROM THE GROUP CONSISTING OF CYCLOTRIMETHYLENETRINITRAMINE AND CYCLOTETRAMETHYLENETETRANITRAMINE; (B) ABOUT FROM 0.5 TO 15% BY WEIGHT OF SOLUBLE NITROCELLULOSE HAVING AN AVERAGE DEGREE OF POLYMERIZATION OF ABOUT FROM 2000 TO 3000; AND (C) ABOUT FROM 10 TO 34.5% BY WEIGHT OF ESTER SELECTED FROM PHOSPHATE AND CARBOXYLATE ESTERS HAVING THE FORMULAS: 